Clamping ring for use in a pipe joint

ABSTRACT

A clamping ring for use in pipe joints has an inside surface which is formed with generally peripherally extending indentations for axially fixing a pipe. In order to prevent an occurrence of dangerous stress concentrations in pipes in contact with such clamping rings and to permit such rings to be manufactured economically, the clamping ring is formed on its inside surface with a multiplicity of generally peripherally extending indentations, each of which extends only along part of the periphery of said inside surface, and said indentations are offset from each other in said peripheral directions and adjoin or overlap.

FIELD OF THE INVENTION

This invention relates to a clamping ring for use in a pipe joint, whichring has an inside surface formed with peripherally extendingindentations. This invention relates also to a process and apparatus formaking such clamping rings.

DESCRIPTION OF THE PRIOR ART

Clamping rings can be used in pipe joints which are adapted to take upaxial loads applied to the pipes and which are not only leakage-proofbut will provide also a thrust-resisting mechanical coupling. Suchclamping rings have a conical outside surface, which cooperates with amating conical inside surface of a pipe socket and by means of suchsocket can be forced onto the outside surface of a pipe. Such clampingrings have a serrated inside surface, which is in pressure contact withthe outside surface of the pipe to hold the pipes against an axialdisplacement. The known clamping rings are formed on their insidesurfaces with annular indentations so that the lands remaining betweenthe annular indentations will apply pressure to the outside surface ofthe pipe and said outside surface will thus be deformed to have annularperipheral grooves. Such a shape of the pipe will result in a highstress concentration, which may cause the pipe to crack under high load.Particularly, pipes made of plastic, such as polyvinylchloride andpolyethylene, which are increasingly used in underground pipelines owingto their resistance to corrosion, are highly susceptible to stressconcentration so that the use of the known clamping rings in jointsbetween such plastic pipes will give rise to difficulties.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a clamping ring which avoidsdangerous stress concentrations in pipes connected by a joint comprisingsuch clamping ring and which ensures that pipes connected by such jointwill be reliably and firmly held in position even when subjected to highaxial loads.

It is another object of the invention to provide a process and apparatusfor an economical manufacture of such clamping rings.

SUMMARY OF THE INVENTION

This object is accomplished in accordance with the invention in that theclamping ring is formed in its inside surface with a multiplicity ofgenerally peripherally extending indentations, each of which has alength which is only a fraction of the peripheral extent of said insidesurface, and laterally adjacent ones of said indentations adjoin oroverlap and are peripherally offset from each other. In such a clampingring, ridges are formed between the indentations so that the insidesurface of the clamping ring is formed with thin, closely spaced apartserrations, which apply pressure to the outside surface of theassociated pipe in small surface portions, which are distributed over alarge surface area whereby dangerous stress concentrations are avoidedbecause there are no peripherally extending, annular indentations.Nevertheless an excellent pressure contact between the clamping ring andthe pipe is ensured by the large number of distributed smallindentations.

A clamping ring may be formed with such indentations in a simple andeconomical process, in which a cutting tool is used to cut theindentations into the inside surface of the clamping ring while thelatter is rotated about its axis. A lathe tool has previously been usedto cut annular peripheral indentations into the inside surface of theclamping ring. In accordance with the invention, a large number ofstaggered indentations are cut into the inside surface of the clampingring by means of a cutting tool, which is subjected to a movementtending to revolve the tool on a circular orbit which is smaller indiameter than the inside surface of the clamping ring and extends in aplane that is transverse to the axis of the clamping ring, and astraight feed movement which is parallel to the axis of the clampingring is simultaneously imparted to the tool. In that operation, acrescent-shaped indentation is cut into the inside surface of theclamping ring by the tool during each revolution thereof and owing tothe straight feed movement of the tool said indentations will extendalong a helix. Mutually offset indentations equal in number to therevolutions of the cutting tool will thus be formed and because therotation of the clamping ring and the straight feed movement of the toolare superposed, said indentations in their entirety will constitute thedesired serrations on the inside surface of the clamping ring. Thepattern of such serrations will depend on the diameter of the insidesurface of the clamping ring, on the number of revolutions per minute ofthe cutting tool, on the diameter of its orbit, as well as on the speedof the clamping ring, the velocity of the feed movement of the tool, theshape of the tool and the depth of cut. The serrations on the insidesurface of the clamping ring can be varied in dependence on theselection or variation of one or more of the parameters stated above. Inthis way, the serrations can be adapted to the desired retainingproperties, to the materials of the pipes and to their surface finish.

It will be particularly desirable to cause the cutting tool to revolvein a plane which is at an acute angle to a normal plane on the axis ofthe clamping ring because the movement of the cutting tool along such aninclined orbit will result in sawtooth-shaped serrations, which willensure an improved fixation of the pipes.

The process in accordance with the invention can be carried out in asuitable manner by means of a lathe comprising a drivable chuck forrotating the clamping ring and a carriage, which is movable along theaxis of the chuck and carries the cutting tool, wherein the carriagecarries a milling unit, which comprises a cutter spindle that extendstoward the chuck and carries a radial cutter tooth which constitutes acutting tool. Such lathe can be provided by a simple alteration of anexisting lathe so that it can be used to carry out the process inaccordance with the invention. During the operation of such lathe, thecutter tooth of the milling unit will cut the several indentationsquickly and without difficulty and the pattern of the serrations canalso be influenced as desired without difficulty. If the cutter spindleextends at an angle to the axis of the chuck, the cutting tool willrevolve along an inclined plane so that the angle of inclination of thecutter spindle and the sawtooth shape of the serrations can be changedby a single adjustment.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a developed view showing the inside surface of a clamping ringaccording to the invention.

FIGS. 2, 3 and 4 are enlarged sectional views taken on lines II--II,III--III and IV--IV, respectively, in FIG. 1.

FIG. 5 is a side elevation showing apparatus for shaping said insidesurface.

SPECIFIC DESCRIPTION

A thrust-resistant pipe joint which is not susceptible to dangerousstress concentrations comprises a clamping ring 1, which is formed inits inside surface 2 with a large number of elongated generallyperipherally extending indentations 3, which are offset from each otherin the peripheral and axial directions and overlap. Owing to theseindentations the inside surface 2 is formed with dense shingledserrations and adjacent indentations are separated by arcuate ridges 4,which like the indentations 3 extend generally peripherally and are alsooffset from each other and form a mesh pattern. In pressure contact withthe outside surface of a pipe, such an inside surface 2 will not deformsaid outside surface to form annular indentations therein so that damageto the pipe due to stress concentration need not be feared.Nevertheless, the large number of indentations 3 and their shingledarrangement result in a strong pressure contact between the clampingring 1 and the outside surface of the pipe so that the pipe will befirmly held against axial displacement.

It is apparent from FIG. 2 that the ridges 4 have different heights in across-sectional plane of the clamping ring 1. This is due to the factthat adjacent indentations 3 overlap.

As is apparent from FIG. 5 a clamping ring 1 may be formed with such aserrated inside surface 2 by means of a simple lathe 5, which comprisesa rotatable chuck 6, which is adapted to be driven, and a carriage 8,which is axially movable by means of a lead screw 7 and carries amilling unit 9. The clamping ring is fixed in the chuck 6 and is shapedon the inside surface 2 of the ring 1 by a radial cutter tooth 11, whichis non-rotatably secured to a cutter spindle 10 of the unit 9. As thespindle 10 rotates, the cutter tooth tends to revolve on a circularorbit and by means of the carriage 8 a straight feed movement that isparallel to the axis of the clamping ring is imparted to the cuttertooth 11. The clamping ring 1 is rotated by the chuck 6 at the sametime. An upward cut is provided in that the cutter spindle 10 and thechuck 6 are rotated in mutually opposite directions. Because therotation of the chuck and the movement of the carriage are superposed,the indentations successively cut into the inside surface 2 of theclamping ring 1 will extend along a helix. The pattern of the serrationsformed on the inside surface 2 of the clamping ring 1 will be determinedby the ratio of the movements described hereinbefore, by the number ofrevolutions per minute of the cutter tooth 11 and by the radius of itsorbit.

For a given diameter of the inside surface, the shape of eachindentation will be determined by the shape of the cutter tooth 11 andby its depth of cut. If the cutter spindle 10 is inclined relative tothe axis of the clamping ring, the indentations will be unsymmetrical incross-section so that the serrations on the inside surface will have asawtooth shape depending on the angle of inclination.

The serrations formed in accordance with the invention on the insidesurface 2 of the clamping ring ensure that a pipe joint provided withsuch clamping ring will resist high axial loads and will have optimumforce-transmitting properties without giving rise to dangerous stressconcentrations. For this reason, clamping rings having such insidesurfaces are particularly suitable for joints between plastic pipes orbetween joints made of other materials which are susceptible to stressconcentrations.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A clamping ring for usein a pipe joint, comprising:an annular body having an annular innersurface engageable with an outer surface of a pipe; and a surface arrayof contiguous indentations in said inner surface for gripping said outersurface of said pipe, said indentations being generally elongated anddefined by arcuate ridges, said indentations and ridges extendinggenerally peripherally of said inner surface with adjacent ridges andindentations in a peripheral direction of said body overlapping oneanother and adjacent indentations in a direction transverse to saidperipheral direction being peripherally offset from one another, each ofsaid indentations having a length which is only a fraction of theperipheral extent of said inner surface whereby a multiplicity of saidindentations lie in end-to-end relationship around the periphery of saidinner surface.
 2. The clamping ring defined in claim 1 wherein saidridges have different heights in a cross-sectional plane through saidring.
 3. The clamping ring defined in claim 1 wherein said ridges form amesh pattern.